Position instrumented blowout preventer

ABSTRACT

A ram of a ram-type blowout preventer is enclosed within an enclosure so that the piston driving the ram is placed parallel to a stationary magnetizable waveguide tube. A transverse ring-like magnet assembly surrounds the tube and is attached to a carrier that, in turn, is attached to the tail of the piston. The magnet assembly longitudinally magnetizes an area of the tube where it is located. A wire running through the tube is periodically interrogated with an electrical current pulse, which produces a toroidal magnetic field about the wire. When the toroidal field intersects with the longitudinally magnetized area, a magnetostrictive acoustical return pulse is reflected back up the tube for detection by a transducer located outside of the enclosure. The time that the acoustical pulse travels from the magnetic field intersection compared to the timing of the electrical pulse on the wire is a measure of distance since the pulse time essentially travels at the speed of light. Thus, the position of the ram is absolutely determined. From the position information from successive pulses, ram velocity and acceleration information can be developed. The measurements are continuous and absolute and are not incremental.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to blowout preventer instrumentation and moreparticularly to the direct measurement of position, velocity, and rateof movement of the parts in a ram type blowout preventer.

2. Description of the Prior Art

Blowout preventers (BOP's) are employed at the wellhead of an oil or gaswell as a safety device for shutting off the flow of fluids from theannulus of the well in the event of excessive build-up of pressure.Although there are many kinds of blowout preventers, one popular classis known as a "ram" type blowout preventer. In this type of blowoutpreventer, the well pipe extends through a central opening in thepreventer housing or block. Guideways, usually two opposing ones, in thehousing of the preventer are located transverse to the axis of the wellpipe. Rams driven by hydraulically actuated pistons operate with respectto these guideways to reciprocate the rams to close off the annulusaround the pipe when there is a need. Shear ram blowout preventersinclude rams having sharp edges for shearing off the pipe, rather thanclosing around it, so that these rams completely shut off the annulusand the pipe opening, as well, when they are closed.

Knowledge of the parameters of the conditions of the well at the blowoutpreventer is extremely important to maintaining proper operation of thewell. From these parameters, the well can be controlled so that safeconditions can be maintained in ordinary circumstances of operation andwhen an unsafe condition is detected that cannot be controlled, shutdown of the well can be appropriately initiated, either manually orautomatically. For example, pressure transducers and temperaturetransducers are used at the blowout preventer to develop signalsindicative of these respective conditions. These and other signals aretypically presented as control signals on a control console employed bya well operator. This operator can, for example, control the operationsof the well by controlling the rotating speed on the drill pipe,controlling the downward pressure on the drill bit, regulating thecirculation pumps for the drilling fluid for a drilling operation and/oradjusting the extent that the annulus is opened or closed by actuatingthe hydraulically actuated pistons connected to the reciprocating rams.

Heretofore, it has not been possible to know precisely the location ofthe rams, even though the operator might be controlling them. Thecontrol operator has had to rely on secondary measurements, such as wellflow, to estimate the positions of the rams. Well flow, however, isaffected by much more than how large the ram gap is. Thus, there hasbeen a need for an improved measure of the ram gap in a more directmanner.

One device that has been employed in the past to develop a signalindicative of the relative position of component parts located in anenclosed housing (not necessarily in a blowout preventer housing) is apotentiometric transducer. Such a device employs one or more sensorsthat are subject to wear and inaccuracies in the presence of a harshenvironment. Moreover, such sensors are subjected to being lifted fromthe surface of whatever is being tracked, which causes inaccuracies.Also, a loss of power often causes distorted readings because thesedevices operate incrementally, adding or subtracting values related tospecific turns or segments of wire to a previous value. Moreover,devices such as these are notoriously poor high speed devices. Thus,potentiometric measurement would not be useful in accurately determiningthe position parameter of ram movement. In addition, since the velocityand rate conditions of ram movement are also important, potentiometricdevices are not useful since they cannot provide, however imperfectly,such information at all.

It is further noted that incremental measuring devices of whatever sortfor only keeping track of steps have the inherent shortcoming of havingto be reset to a baseline in the event of a power failure as well as notproviding the precision that is attendant to continuous measurement.

Therefore, it is a feature of the present invention to provide animproved apparatus for precisely measuring the location or position of aram or ram piston in a blowout preventer.

It is another feature of the present invention to provide an improvedinstrumentation device that continuously and absolutely determines theposition of a ram or a ram piston in a blowout preventer and which doesnot have to be reset in the event of power failure.

SUMMARY OF THE INVENTION

The instrumentation device of the present invention incorporates thecomponents of a magnetostrictive linear displacement arrangement incombination with the components of a ram type blowout preventer. A ramin a blowout preventer is located in a guideway transverse to thecentral pipe-receiving bore or opening of the preventer and reciprocatesto close and open on this central bore. A ram is motivated by ahydraulic piston located within the overall housing of the blowoutpreventer. An elongated magnetizable magnetostrictive waveguide tube isplaced in a cylinder head enclosure connected to the preventer housingfor accommodating the movement of the ram piston. The tube, which issealed and capable of sustaining 4,500 psi of hydrostatic pressureexerted by the closing pressure of the ram BOP, is placed parallel tosuch piston movement. A ring-like magnet assembly is also located withinthe enclosure and is positioned around the tube. This assembly isattached or connected to a carrier that is, in turn, connected to thetail of the piston. The magnet assembly includes typically fourpermanent magnets in a plane transverse to the axes of the piston andthe tube. These individual magnets are circumferentially evenly spacedaround the tube and are located at a uniform distance from the tube. Thering-like assembly is set apart from engaging the surface of the tubeand is mounted to move axially along the tube without touching it.

A conducting wire is located within the waveguide tube for periodicallyreceiving an interrogation current pulse, which current pulse produces atoroidal magnetic field around the wire and in the tube. When thistoroidal magnetic field encounters the longitudinal magnetized area ofthe waveguide tube, a helical sonic return signal is produced in thewaveguide tube. A magnetostrictive receiving transducer located outsideof the housing is connected through the housing to the waveguide tubefor sensing the helical return signal and producing an electrical signalto a meter or other indicator as an indication of the position of thering-like magnet assembly and, thus, the piston. Precisely locating thepiston also results in precisely locating the position of the ram. Inaddition, from the information provided by additional pulses and thetiming of such pulses, the velocity and the rate of movement of the ramcan also be determined.

The packer wear surface of the ram that makes contact with the outsideof the well pipe is critical to the sealing of the annulus. When thepacker wear pads are new, the closed position of the ram can bedetermined in the manner described above. After the ram has been used,the closed position of the ram with respect to the historical originalposition is an indication of the amount of wear on the wear pads orpacker. If a worn wear pad can be replaced while the well is otherwiseshut down, and before it fails in service, then costly shut-down of thewell at an inconvenient time or damage caused by failure can be avoided.Other uses of the exact precision position, velocity and rateinformation can be made by the well operator.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features, advantages andobjects of the invention, as well as others which will become apparent,are attained and can be understood in detail, more particulardescription of the invention may be had by reference to the exemplaryembodiments thereof that are illustrated in the drawings, which drawingsform a part of this specification. It is to be noted, however, that theappended drawings illustrate only typical preferred embodiments of theinvention and are therefore not to be considered limiting of its scopeas the invention may admit to other equally effective embodiments.

In the drawings:

FIG. 1 is a pictorial oblique view of a typical ram-type blowoutpreventer with which the current invention is used.

FIG. 2 is a cross-sectional view of a portion of a blowout preventer inaccordance with a preferred embodiment of the present invention, thepreventer being shown in its closed position.

FIG. 3 is a cross-sectional view of the same portion of the blowoutpreventer as that shown in FIG. 2, the preventer being shown in its openposition.

FIG. 4 is a close-up view of part of FIG. 3.

FIG. 5 is a schematic diagram of the magnetic and magnetostrictiveforces present in operation of the present invention.

FIG. 6 is a graphic representation of the closing of a shear ram.

DESCRIPTION OF PREFERRED EMBODIMENTS

Now referring to the drawings, and first to FIG. 1, a ram-type blowoutpreventer 10 is illustrated. A well pipe 12, which can be part of adrill string located at the top of a well being drilled or a part of aproduction string of a well under oil or gas production, is shownpassing through a center bore or opening 14 in the housing or block 16of the blowout preventer. The block includes opposing guideways 18transverse to opening 14, which guideways extend outwardly into bonnets17 connected to block 16. Operating in guideways 18 are rams 20 drivenby hydraulic pistons 22 in their respective cylinder liners 23 locatedin respective cylinders 19 connected outwardly of bonnets 17. Thepistons reciprocate the rams back and forth in the guideways and to openand close packers or wear pads 24 in the faces of rams 20 with respectto the surface of pipe 12. The hydraulic fluid connections are not shownspecifically in the drawing, but are well known in the art, and operatein connection with opening chamber 25 and closing chamber 26. The tailof the piston reciprocates within a cylinder head 19, bolted to a bonnet17.

It is desirable to exactly know or to locate the position of rams 20.This is accomplished by separating the parts of a magnetostrictivelinear displacement device to locate some of the components within acylinder head enclosure 30, shown in FIGS. 2 and 3, which connect tocylinder 19 shown in FIG. 1. As will be explained below and shown inFIG. 4, a transducer 32 located on the outside of enclosure 30 isconnected to the internal parts of the device through end cap 34attached to the cylinder head enclosure 30. Transducer 32 produces anelectrical signal to a meter or other indicator and/or to a controlconsole.

Now referring to FIG. 5, a schematic representation of amagnetostrictive linear displacement device is shown. Magnetostrictionrefers to the ability of some metals, such as iron or nickel oriron-nickel alloys, to expand or contract when placed in a magneticfield. A magnetostrictive waveguide tube 36 has an area within anexternal magnet assembly 38 that is longitudinally magnetized asassembly 38 is translated longitudinally about tube 36. Assembly 38includes typically four permanent magnets 40 located at evenly spacedpositions 90° apart from each other, in a plane transverse to tube 36,and radially equally spaced with respect to the surface of tube 36. Morethan four magnets can be used, if desired. External magnetic field 42 isestablished, which as previously mentioned, longitudinally magnetizes anarea of tube 36.

Tube 36 surrounds a conducting element or wire 44 located along itsaxis, which wire is periodically pulsed or interrogated with anelectrical current in a manner well-known in the art. Such a currentproduces a toroidal magnetic field 46 around wire 44 and tube 36. Whentoroidal magnetic field 46 intersects with field 42 at positions 48, ahelical magnetic field is induced in tube 36 to produce a sonic pulsethat travels toward both ends of the tube. Suitable dampers, not shown,at the ends prevent echo reverberations of the pulse from occurring.However, at the transducer end or head, the helical wave is transformedto a waveguide twist 48, which exerts a lateral stress in very thinmagnetostrictive tapes 50. A phenomenon known as the Villari effectcauses flux linkages from magnets 52 running through sensing coils 53 tobe disturbed by the traveling stress waves in the tapes and to develop avoltage across the coils. This voltage is subsequently amplified formetering or control purposes.

Because the current pulse travels at nearly the speed of light, and theacoustical wave pulse travels roughly at only the speed of sound, a timeinterval exists between the instant that the head-end transducerreceives each pulse compared with the timing of the electrical pulseproduced by the head-end electronics. This time interval is a functionof the distance that external magnet assembly 38 is from the head end ofthe tube. By carefully measuring the time interval and dividing by thetube's velocity of propagation, the absolute distance of the magnetassembly from the head end of the tube can be determined.

It is well-known that the acoustic waveguide tube is made of materialsespecially temperature stable. Therefore, such a tube is especiallyappropriate for use in the instrumentation described below in a blowoutpreventer application.

Returning to FIGS. 2, 3 and 4, piston 22 is shown in its fully closedposition in FIG. 2 and is shown in its fully opened position in FIG. 3.A carrier 54, especially easily seen in FIG. 4, for magnet carrier 38 isattached to piston tail 56 via retainer 58 and screw 60.

Stationary waveguide tube 36 is located within cylinder head 30 parallelto the axis or the center line of the piston tail and is spacedtherefrom so as not to interfere with the movement of piston 22.Ring-like magnet assembly 38 is located about and spaced apart from tube36 and is located at a distance from carrier 54 determined by spacer 62.The magnets in the assembly are in a plane transverse to tube 36.Non-magnetic screws 64 are used to mount magnet assembly 38 and spacer62 to carrier 54. It will be seen that carrier 54 along with spacer 62and assembly 38 are shown in two positions. In FIG. 2, assembly 38 is inits fully closed position and assembly 38 is in its fully open positionin FIG. 3. It should be noted that as carrier 54 translates from left toright, there is no contact, and thus no wear, of assembly 38 or thesurface of tube 36.

Conducting element or wire 66 is located through the center of waveguidetube 36. Both wire 66 and tube 36 are connected to transducer 32,located external to cap 34, which transducer assembly also includessuitable means for placing an interrogation electrical current pulse onwire 66. An O-ring 68 is used to seal end cap 34 against leaks.

It may be noted that as ram 20 moves axially, assembly 38 will be movedby the same amount. Thus, by the operation of the magnetostrictivelinear displacement device incorporated therewith, it is possible toabsolutely determine on a continuous basis the position of ram 20. Inthe event of loss of signal, there is no loss of information orre-zeroing or re-homing of any reading. The reading is absolutelydetermined by the location of assembly 38 with respect to transducer 32,as discussed above in connection with FIGS. 2, 3 and 4.

With the knowledge of the absolute position of the ram, it can bedetermined if the ram is completely closed, if the ram is hung up, towhat degree the packer or wear pad on the front of the ram is worn, andto what degree there is backlash or wear in the piston mechanism. Fromsuccessive interrogation pulses, it is also possible to measure pistonclosing speed or velocity and the rate of movement or acceleration anddeceleration of the piston.

It should be noted that the position, velocity and accelerationinstrumentation that has been described has only one moving part, magnetassembly 38, and this is a non-contacting part. Thus, there is no wearproblem.

It has previously been mentioned that the information provided in thepast for operating a blowout preventer has primarily been pressurereadings. FIG. 6 illustrates closing pressure 70 on the closing side ofa shear ram and, on the open side, opening pressure 72 of the ram as ramgap 74 is measured in accordance with the present invention. Bothpressures are substantially uniform until the shear ram of the preventermakes contact, at which time the closing pressure jumps up. The closingpressure again stabilizes after the pipe is severed until the annulus issealed. Then, the closing pressure reaches its maximum level. Althoughthere is meaningful information provided in the pressure signals, thereis more information provided in the ram gap signal in accordance withthe present invention. Probably the most information is provided byhaving both pressure and ram position information provided to theoperator.

While position instrumentation of one ram of a blowout preventer hasbeen shown and described, it is possible, if desired, to independentlyinstrument both rams of the blowout preventer. Also, the instrumentationof only one type of blowout preventer has been shown in FIG. 1 andanother described in connection with FIG. 6, it will be understood thatthe invention is not limited to a single type, but can be employed withany type of ram blowout preventer. Since many modifications may be madeand will become apparent to those skilled in the art, it will beunderstood that the invention is not limited only to the embodiments ofthe invention that have been described and illustrated.

What is claimed is:
 1. Ram positioning instrumentation includingmagnetostrictive linear displacement measuring means for continuouslyand absolutely locating the position of a ram in a well head blowoutpreventer, the preventer includingan enclosed housing having a verticalbore to receive a well pipe and opposed guideways extending from thebore, rams reciprocal within the respective guideways for opening andclosing the vertical bore, and movable hydraulic pistons connected forpositioning the respective rams, said instrumentation, comprising withinthe enclosed housinga longitudinally magnetized magnetostrictivewaveguide tube parallel to a first one of the movable hydraulic pistons,a plurality of permanent magnets evenly positioned in a transverse planearound said waveguide tube and uniformly spaced apart therefrom forlongitudinally magnetizing a small area of said waveguide tube, saidplurality of permanent magnets being in a fixed position with respect tothe first movable hydraulic piston, and a conducting wire inside of saidwaveguide tube for receiving an interrogation current pulse, saidinterrogation pulse generating a moving toroidal magnetic field aroundsaid wire and a helical return signal in said waveguide tube when thetoroidal field encounters the longitudinal magnetized area of saidwaveguide tube, and external to the enclosed housinga magnetostrictivesensing transducer for continuously determining from the helical returnsignal the absolute location of the ram motivated by the first movablehydraulic piston and producing an electrical metering or control signal.2. The method of determining the location of a ram in a well headblowout preventer, which comprisespositioning a longitudinallymagnetized magnetostrictive waveguide tube alongside and parallel to thetravel path of a piston that drives a preventer ram, affixing to thedriving piston a plurality of permanent magnets evenly spaced around andin a plane transverse to the waveguide tube so that as they travelforward and back with the closing and opening of the driving piston theylongitudinally magnetize a small area of the waveguide tube, pulsing aconductive wire located inside the waveguide tube to generate a movingtoroidal magnetic field around the wire to produce a helical returnsignal in the tube when the toroidal field encounters the longitudinallymagnetized area of the tube, continuously magnetostrictively sensing thehelical return signal to absolutely determine the location of thedriving piston as it closes and opens.
 3. The method of determining thevelocity of a ram in a well head blowout preventer, whichcomprisespositioning a longitudinally magnetized magnetostrictivewaveguide tube alongside and parallel to the travel path of a pistonthat drives a preventer ram, affixing to the driving piston a pluralityof permanent magnets evenly spaced around and in a plane transverse tothe waveguide tube so that as they travel forward and back with theclosing and opening of the driving piston they longitudinally magnetizea small area of the waveguide tube, pulsing a conductive wire locatedinside the waveguide tube to generate a moving toroidal magnetic fieldaround the wire to produce a helical return signal in the tube when thetoroidal field encounters the longitudinally magnetized area of thetube, continuously magnetostrictively sensing the helical return signalto absolutely determine the location of the driving piston as it closes,and determining the velocity of the driving piston from the locations ofits positions over a period of time as the driving piston closes.
 4. Themethod of determining the closure rate of a ram in a well head blowoutpreventer, which comprisespositioning a longitudinally magnetizedmagnetostrictive waveguide tube alongside and parallel to the travelpath of a piston that drives a preventer ram, affixing to the drivingpiston a plurality of permanent magnets evenly spaced around and in aplane transverse to the waveguide tube so that as they travel forwardand back with the closing and opening of the driving piston theylongitudinally magnetize a small area of the waveguide tube, pulsing aconductive wire located inside the waveguide tube to generate a movingtoroidal magnetic field around the wire to produce a helical returnsignal in the tube when the toroidal field encounters the longitudinallymagnetized area of the tube, continuously magnetostrictively sensing thehelical return signal to absolutely determine the location of thedriving piston as it closes, and determining the rate of closure of thedriving piston from the locations of its positions over a period of timeas the driving piston closes.